Methods of and apparatus for the production of high vacua



W. BECKER July 16, 1963 METHODS OF AND APPARATUS FOR THE PRODUCTION OF HIGH VACUA Filed March 9. 1960 INVENTOR! MLL: BEzze Attorneys United States Patent 3,098,155 METHODS 0F AND APPARATUS FOR THE PRGDUQTI$N 0F HEGH VACUA W lli Becker, Ehringshausen, Kreis Wetzlar, Germany, assrgnor to Arthur Pfeiffer G.m.b.H., Wetzlar, Germany Filed Mar. 9, 1960, Ser. No. 13,894 Claims priority, application Germany May 29, 1959 9 Claims. (Cl. Kath-69) This invention relates to a method and an apparatus for the production of high vacuum according to the getter principle.

According to one known proposal, in high vacuum pumps which operate according to the getter principle small amounts of a quantity of metal, preferably titanium, located in the pump casing are vaporised at suitable intervals, and thus there are continuously provided fresh gas-absorbing metallic surfaces. In these pumps the quantity of metal itself must be renewed from time to time. For this purpose it is necessary that the pump should be subjected to atmospheric pressure. in this connectiou, however, the inner surface of the pump becomes charged with gases, which can again be removed only by a lengthy period of pumping. This is undesirable. Furthermore, the pump also cannot be heated as required after a certain period of operation, as in consequence of this heating operation the gases bound by the surfaces would in part again be released.

According to a further known proposal, a solid metal or metal strip is conducted through the pump casing, and thereupon through a second casing, in which the gases picked up by the metal strip in the pump chamber are again released by heating of the strip. However, the passage of the strip from one casing to the other necessitates a gap by means of which a certain quantity of gas flows back in undesirable fashion into the pump chamber. Also, difficulties are caused by a cooling of the strip before its return into the pump chamber.

The method according to the invention operating according to the getter principle avoids the known difliculties. According to this method there is employed as gas-absorbing medium a metal which is liquid at low temperatures and is maintained at a low temperature, and which has a very low vapour pressure even at a comparatively high temperature, preferably gallium or gallium alloys. The liquid metal falls through the casing of the pump with a large free surfaw, preferably in the form of a drizzle. The metal changed with gas is discharged from the pump casing, heated to a temperature sufficiently high for release of the gas, degassed in the heated condition in a second casing maintained under a high vacuum, and after its degassing and cooling to a low temperature again conducted to the pump casing. A high vacuum pump operating according to this method is not attended by difficulties in sealing, as the liquid metal itself may act as a seal. The heating and cooling of the metal may be readily carried out and is preferably effected in a heat exchanger, which is traversed by degassed metal and metal to be degassed. The degasification may also in this way take place in economical fashion at very high temperatures. It is furthermore possible to connect together the two separate casings, i.e., the pump casing and the casing serving for degasification, by means of a pipe socket and to close off the latter by an immersion bell, which is sealed by the liquid metal itself. This has the advantage that the high vacuum pump connected to the second casing may also be employed for producing the vacuum in the pump casing or in the apparatus connected thereto.

The method together with a pump suitable for carrying out this method will now be described in the following with reference to the accompanying drawing, which 3,098,155 Patented July 16, 1963 ice shows by way of example a section through a form of embodiment of the invention.

The pump comprises two casings shown at 1 and 2. The casing 1 is the actual pump casing, to which is connected the apparatus or vessel (not shown) to be evacuated. The casing 1 is constricted in conical fashion at 3 and forms a pipe socket 4 carrying a flange 5 for attachment of the apparatus to be evacuated or of the pipe leading to such apparatus. In the upper part of the casing 1 there are provided vertically to the perpendicular axis of the casing 1 and concentrically to one another three circularly bent pipes 7, which are connected together by pipe sockets 6 and are also connected to a feed pipe 8, which passes through the wall of the casing 1. The pipes 7 are finely perforated over their length, the individual perforations being shown at 10. Liquid metal passes on through these perforations in the form of a rain, as indicated in broken lines. The metal employed preferably comprises gallium or gallium alloys, which are already in a liquid state at low temperatures of approximately 30 C. The metal accumulates on the sloping bottom 11 of the casing 1. At the lowest point of the bottom 11 there is secured a discharge pipe 12 bent in the form of an S-bend. This bend extends beyond the highest level of the metal accumulating on the bottom 11, acting at the same time as a vacuumproof seal for the pump casing 1.

In the casing 2 there is located a cylindrical container 13 having a pipe section 14- which passes through the same and also through the shell of the casing 2 and carries a flange 15 for connection to a high vacuum pump. The latter maintains a high vacuum in the container 13, and accordingly also in the casing 2, as the section 14 also connects the interior of the container 13 with that of the casing 2. In the container 13 there is located a helically wound open channel 16, which terminates above the bottom 17 of the container 13. Liquid metal is conducted to this channel at the highest point through a pipe 18. The metal accumulating on the bottom of the container flows through a pipe 19 in the bottom. 17 to a heat exchanger 20, which is connected on the one hand to the pipe 18 and on the other hand by a pipe 21 to the bend 12 of the casing 1. The pipe 19 traverses the heat exchanger and in similar fashion to the pipe 21 is passed in gastight manner through the casing 2. It carries outside of the casing a cooler 22 andleads to a pump 23, which conveys the metal through the pipe 24 to the pipe 8, and accordingly to the pipes 7.

The shell of the container 13 carries a heating element 25, which surrounds the channel system 16, and above this system cooling pipes 26. The casing '2 in similar fashion to the casing 1 is constricted inconical form at the top and carries a socket 27, which passes in gastight fashion through the bottom 11 of the casing 1 and terminates above the level of the liquid. It is sealed off by means of an immersion bell 28, which together with the ring 29 secured to the bottom 11 forms a liquid seal. The bell 28 is secured to an angle lever 30 having an armature 31, which may be attracted by a magnet 32 secured to the outside of the casing. Thus the bell 28 may be opened and closed by actuation of the magnet 32.

The operation of the pump is as follows, it being assumed that to the flange 5 there is connected the apparatus to be evacuated and to the flange 15 of the casing 2 a high vacuum pump. With the bell 28 opened there is first produced with the high vacuum pump a high vacuum in the casing 2 and accordingly also in the casing 1 and in the connected apparatus. The bell 28' is then closed and the pump 23 is set into operation, that is liquid metal is passed at low temperature through the pipe 24 to the pipes 7. There emerges from the perforations 10 a drizzle of liquid metal, which accumulates on the bottom 11 of the vessel and flows through the pipe 21 to the heat exchanger 20. In stationary operation the metal is heated therein to approximately 600 C., and it passes at approximately 630 C. into the helical channel 16. During its passage through the channel it is heated by the heating element 25 by roughly a further 70 C. to approximately 700 C. At this temperature it enters the heat exchanger 20, is cooled therein by approximately 600 C., i.e., by the amount of heat taken up by the cold metal, and then passes into the cooling jacket 22, in which it is cooled by the temperature taken up by the heating element 25, so that it again flows to the pump 23 at a temperature of 30 C. The metal passing out at low temperature from the pipes 7 absorbs, after establishment of the high vacuum, the gases still contained in the connected apparatus. The metal charged with gas and heated in the heat exchanger and by the heating element discharges the gases in the container 13, from which they are sucked off by the connected high vacuum pump.

Any condensing metal vapours are deposited on the inner wall of the casing 13, which is cooled by the pipes 26, condense and pass again as liquid metal into the channel 16. The heating element 25 is so dimensioned that the heat exchange system is just balanced at the desired temperature, for example at approximately 700 C. when employing gallium.

I claim:

1. Apparatus for attaining a high vacuum in a vessel by the getter principle, comprising two communicating casings of which one is adapted to be connected with a vessel to be evacuated and the second casing is adapted to be connected with a high vacuum pump, means operable to deliver to the first-mentioned casing a liquid metal selected from the group consisting of gallium and a gallium alloy to expose the liquid metal to gas contained in the first-mentioned casing when a vacuum is maintained therein by said high vacuum pump when connected to the second casing whereby gas is absorbed by the liquid metal, means to deliver a gas-charged liquid metal from the first-mentioned casing to the second-mentioned casing, means cooperating with the second-mentioned casing to effect degassing of the gas-charged liquid metal delivered thereto, and means included in said first mentioned means to return the degassed liquid metal to the first-mentioned casing.

2. Apparatus according to claim 1, wherein a pipe socket is provided to form communication between the casings and extending from the second casing through the bottom of the first casing, and in which a ring in the bottom of the first casing and an immersion bell are provided to cover the opening of the socket into the firstmentioned casing and being movable relative to said opening, and cooperates with the ring extending upwards from the bottom of the first-mentioned casing so as to eflect a liquid seal with gas-charged liquid metal contained at the bottom of the first-mentioned casing for delivery to the second-mentioned casing.

3. Apparatus according to claim 1, in which an overflow is provided in the bottom of the first-mentioned casing for discharge of the liquid metal, said overflow being an S-shaped bend which seals the second-mentioned casing in gas-tight manner.

4. Apparatus according to claim 1, wherein the means operable to deliver liquid metal to the first-mentioned casing includes a pipe system comprising finely perforated pipes and a feed pipe for the liquid metal for distribution of the liquid metal.

5. Apparatus according to claim 1, wherein the means for degassing gas-charged liquid metal comprises a container housed in the second-mentioned casing, a helically wound channel located in the container, pipe connections to supply liquid metal from the first-mentioned casing to said channel and to discharge liquid metal from the channel, and a heating element surrounding the container to effect heating of liquid metal in the channel.

6. Apparatus according to claim 1, a heat exchanger is provided and wherein the means for degassing gascharged liquid metal comprises a container housed in the second-mentioned casing, a helically wound channel located in the container, pipe connections to supply liquid metal from the first-mentioned casing to said channel and to discharge liquid metal from the channel, a heating element surrounding the container to effect heating of liquid metal in the channel, and said second-mentioned casing housing the heat exchanger connected with said pipe connections.

7. Apparatus according to claim 1, in which pipes, a cooler and a pump are provided wherein the first and second-mentioned casings are connected together by the pipes for the supply and discharge of the liquid metal, and in the supply pipe for degassed metal leading to the firstmentioned casing there are provided the cooler and the pump.

8. Apparatus according to claim 1, wherein the means for degassing gas-charged liquid metal comprises a container housed in the second-mentioned casing, 21 helically wound channel located in the container, pipe connections to supply liquid metal from the first-mentioned casing to said channel and to discharge liquid metal from the channel, a heating element surround the container to effect heating of liquid metal in the channel, and in which a cooling system is provided to surround the container above the channel for the liquid metal.

9. Apparatus according to claim I, wherein a pipe socket is provided to form communication between the casings and extending from the second casing through the bottom of the first casing, and in which a ring in the bottom of the first casing and an immersion hell are provided to cover the opening of the socket into the first-mentioned casing and being movable relative to said opening, and cooperates with the ring extending upwards from the bottom of the first-mentioned casing so as to effect a liquid seal with gas-charged liquid metal contained at the bottom of the first-mentioned casing for delivery to the second-mentioned casing, and in which a magnet is provided secured on the outside of the firstmentioned casing to open and close the immersion bell.

No references cited. 

1. APPARATUS FOR ATTAINING A HIGHA VACCUM IN A VESSEL BY THE GETTER PRINCIPLE, COMPRISING TWO COMMUNICATING CASINGS OF WHICH ONE IS ADAPTED TO BE CONNECTED WITH A VESSEL TO BE EVACUATED AND THE SECOND CASING IS ADAPTED TO BE CONNECTED WITH A HIGH VACUUM PUMP, MEANS OPERABLE TO DELIVER TO THE FIRST-MENTIONED CASING A LIQUID METAL SELECTED FROM THE GROUP CONSISTING OF GALLIUM AND A GALLIUM ALLOY TO EXPOSE CONSISTING OF GALLIUM AND GALIN THE FIRST-MENTIONED CASING WHEN A VACUUM IN MAINTAINED THEREIN BY SAID HIGH VACUUM PUMP WHEN CONNECTED TO THE SECOND CASING WHEREBY GAS IS OBSORBED BY THE LIQUID METAL, MEANS TO DELIVER A GAS-CHARGED LIQUID METAL FROM THE FIRST-MENTIONED CASING TO THE SECOND-MENTIONED CASING, MEANS COOPERATING WITH THE SECOND-MENTIONED CASING TO EFFECT DEGASSING OF THE GAS-CHARGED LIQUID METAL DELIVERED 